- Sipple's syndrome (medullary thyroid carcinoma-pheochromocytoma) 193
- Sirenomelia 759.89
- Siriasis 992.0
- Sirkari's disease 085.0
- SIRS (systemic inflammatory response syndrome) 995.90
- Siti 104.0
- Sitophobia 300.29
- Situation, psychiatric 300.9
- Situational
- Situs inversus or transversus 759.3
- Sixth disease 057.8
- Sjögren (-Gougerot) syndrome or disease (keratoconjunctivitis sicca) 710.2
- Sjögren-Larsson syndrome (ichthyosis congenita) 757.1
- Skeletal - see condition
- Skene's gland - see condition
- Skenitis (see also Urethritis) 597.89
- Skerljevo 104.0
- Skevas-Zerfus disease 989.5
- Skin - see also condition
- SLAP lesion (superior glenoid labrum) 840.7
- Slate-dressers' lung 502
- Slate-miners' lung 502